1. Field of the Invention
The invention relates to a vehicle occupant restraint system that restrains an occupant, seated in a seat, to the seat at least in the event of a collision.
2. Description of the Related Art
There is known a seat belt that includes a pair of left and right lap belt retractors that retract left and right lap belts and a pair of left and right shoulder belt retractors that retract left and right shoulder belts, in which the retracting forces of the lap belt retractors are set to be larger than the retracting forces of the shoulder belt retractors (for example, see Japanese Patent Application Publication No. 2004-330975 (JP-A-2004-330975)). According to the JP-A-2004-330975, this configuration prevents the lap belts from being raised by the retracting forces of the shoulder belts.
However, in the above described existing technique, when the belts are forcibly retracted in the event of a vehicle collision, the lap belt retractors retract the lap belts against the retracting forces of the shoulder belt retractors. Therefore, in order to ensure readiness, the lap belt retractors each need to have a large driving source that is able to generate a large driving force.
In addition, not only when the belts are retracted by the retractors but also when a gas generator of a pretensioner provided at each anchor support portion that fixes the lap belt is activated to draw the lap belt or when an airbag provided for each lap belt is inflated to apply tension to the lap belt, the tension should be applied to each lap belt against the tension applied to each shoulder belt. Therefore, in any cases, it is necessary to generate a large gas pressure.